Just a light touch from a stranger can stimulate a surge in a woman's body temperature, especially if the person making contact is a man, psychologists found.

Researchers used thermal imaging and saw that even the simplest social contact, like being briefly touched on the hand or on the face, is enough to create a small but significant increase in the facial temperature of female volunteers.

Additionally, scientists from the University of St Andrews found that women's facial temperatures increased more during interactions with a male compared to a female, and a two-second touch on 'high-intimate locations' like on the face and chest, stirred a greater rise in temperature than being touched on the arms and palms.

Investigators recruited 16 heterosexual female participants aged 19 to 24, who thought they were having their skin color measured with a small flashing light device. Researchers secretly took thermal images of the participants' faces as they pretended to measure participant skin color in four different places using the hand held plastic device.

The findings show that across all situations, a touch was found to produce an average shift in temperature of about 0.1°C, but the change was significantly more pronounced when "personal" areas of the body, such as the face and chest, had physical contact and was effect was even more prominent when the researcher was male rather than female.

Researchers writing in the Royal Society journal Biology Letters said that the latest findings confirm previous research that showed that face and body temperature increases during sexual arousal. For example men's skin rises in temperature when they are sexually excited.

However, fear and stress has also been found to raise facial temperature. Stress caused by lying or performing difficult mental tasks also increases skin temperature on the forehead and around the eyes.

Researchers said that in past studies facial redness has been shown to make people appear more attractive, and even when the face shows no color change the changes in facial temperature can still be detected by others through touch or even smell. 

The rise in body temperature can serve as either a signal to the individual themself for them to change their own behavior, or could act as social cues for others. 

"We find that tactile contact elevates facial temperature, even when touch is an incidental part of laboratory procedure," researchers led by Amanda Hahn, from the University of St. Andrews in Scotland wrote in the study. "Whether the changes measured in this study are detectable by others is currently unknown. If such changes in facial temperature during social contact are detectable (by observers or the individual), they could act as social cues."

"Slight increases in facial skin redness are perceived as more attractive, so it may be the case that temperature changes impact perceived attractiveness, although whether or not the skin temperature changes in interactions such as those studied here lead to detectable changes in redness and attractiveness remains to be determined," researchers concluded.

The study was published May 30 in the Biology Letters.